unlocking means to have the cellphone whether cdma (no sim card) or GSM (sim card) to work on other networks

for example:

making a blackberry storm UNLOCKED to work on sprint network

sometimes certain features cant be used though so thorough knowledge of the phone helps

The only problem with that is that Sprint will not accept unlocked devices on their network. This is where it gets complicated, and confusing. For the most part, unlocking refers to GSM devices, or phones with GSM capabilites, like the Tour, Storm, etc. These can be unlocked to be used on GSM networks, like Rogers, T-Mobile, AT&T, etc. You cannot "unlock" a Verizon phone to work on Sprint, as Sprint will not accept the ESN. Verizon will not take other providers devices either. They could be flashed to work with other providers, like MetroPCS and Cricket, but that won't always work either.